This invention relates to appliance timers and, particularly, to an appliance timer having a dual frequency drive.
Although the principles of the present invention may be included in various timers, a particular application is made in timers of the type employed to control the various circuits and functions of automatic laundry appliances such as washers and dryers. Appliance timers basically comprise a rotatable member having a plurality of projecting cams which sequentially engage switch members which control the various operations of the appliance.
Basically there are two types of timers for home appliances. One such timer is a cylindrical rotary drum having a plurality of cams projecting from its surface which engage switch members and is quite similar to a music box. A principal disadvantage of such a timer is that it is bulky and it is difficult to mount the timer in the limited space requirements dictated by the appliance manufacturer. A more acceptable timer as far as space requirements are concerned is the timer set forth in U.S. Pat. No. 2,703,347 to A. R. Constantine, issued Mar. 1, 1955. According to that patent, the appliance timer comprises a flat disk mounted in a housing and having ratchet teeth on its periphery. The disk is driven incrementally about a central shaft by a pawl, which in turn is driven in a reciprocal manner by a synchronous motor. At least one face of the disk is provided with arcuate cam surfaces which are concentrically arranged about the face or faces of the disk. Switch members are arranged about the faces of the housing to engage the arcuate cam members upon rotation of the disk. Electric connectors cooperate with the switch members to control the various cycles of the appliance.
It is desirable that the disk be driven at a very slow rate of advance, since one rotation of the disk should complete at least one entire cycle of the machine. It is also desirable that the disk be driven at a higher rate of advance during switching operations to increase the accuracy of those operations and to decrease arcing, since slow make-break switching promoters arcing and therefore, increased switch wear.